The dry mill production of ethanol is well known in the Prior Art. In FIG. 1, there is shown one exemplary illustration of such a process in accordance to the prior art. First, corn 10 is mechanically grinded 15. The ground corn is mixed with water and enzymes in a steeping process 20 which creates a “mash”. The mash is heated with yeast to promote fermentation 25 of the starches from the corn into ethanol. The fermented mash is distilled 30 and the ethanol is extracted 40. The now spent mash is dewatered and dried 35 to create distillers dried grains and solubes (DDGS) 50. The DDGS 50 is then sold or consumed by animals as feed stock.
The production of ethanol involves significant use of natural gas 45 (35,000-40,000 BTU/gallon of ethanol produced) and approximately a third of the natural gas consumed in the current ethanol process is used in the last step, to dry the mash to create a sellable product, DDGS. Moreover, the drying of the spent mash from the ethanol process to create the DDGS disadvantageously produces the emission of volatile organic compounds (VOC) 55.
While ethanol has become part of the United States' strategy to develop alternative fuels to eliminate reliance on oil and natural gas, there is significant controversy over whether or not it takes more energy, currently non-renewable energy, to produce a gallon of ethanol than the energy value of that gallon of ethanol. The most recent evaluation from the US Department of Agricultural concludes that ethanol has a positive net energy value (i.e., ethanol energy content—energy required for ethanol production); a significant increase in the net energy value for ethanol would accelerate its acceptance as an alternative fuel and its share of the liquid fuels market.
In one prior art reference, U.S. Pat. No. 6,355,456 discloses a process of using wet grain residue from ethanol production to feed livestock. The manure collected from livestock is used for the production of methane. The '456 patent produces wet distiller's grains and solubles, (hereinafter “WDGS”) as a co-product of ethanol production. The WDGS is mixed with grain to produce cattle feed, which is fed to cattle in special barns with slatted floors in order to grow cattle and produce manure. The manure is placed into an anaerobic digester, where the manure is microbially converted to methane. The '456 patent further mechanically separates solids and liquids in the sludge from the manure, dries the solids, and sells the digested liquid and dry solids. The '456 further uses heat produced from the biogas combustion for dry milling the grain.
While the '456 patent has some advantages, it also has some disadvantages. For example, the livestock actually remove much of the energy and ammonia that are present in the WDGS, which could be recovered and used. The WDGS is used to feed and grow the cattle, rather than try to convert the WDGS to energy. The present invention improves upon the teachings of the '456 patent and provides for even greater advantages over the '456 patent, discussed in detail below.